Presently, three types of hot stick electrical measurement equipment are available for performing spot measurements. A hot stick voltmeter measures the voltage between a medium voltage (MV) line and ground, typically using a resistive voltage divider. A typical example is the instrument described at http://www.rossengineeringcorp.com/hi-z_hv_voltmeters.htm incorporated herein by this reference. The device connects to the line and has a connection to ground.
A hot stick ammeter measures the current flowing in a MV line, typically using an air-cored coil as the sensor. A typical example is the instrument described at http://www.hdelectriccompany.com/assets/files/halo_im.pdf incorporated herein by this reference. These devices typically have no connection to ground.
A hot stick power quality meter is essentially a hot stick ammeter augmented with a non-contact capacitive or fiber optic voltage gradient sensor that does not require a connection to ground. The voltage gradient sensor is not accurate enough to measure the voltage amplitude with accuracy, but it is claimed that voltage phasing information from the sensor can be used to accurately determine power factor and provide power quality information such as total harmonic distortion. A representative device is described at: http://tinyurl.com/qualstick incorporated herein by this reference.
These devices have several shortcomings including low accuracy of voltage measurements. Resistive voltage dividers are polluted by stray capacitance. In practice, no portable hot stick volt meters with accuracy better than 1% is available for purchase.
In contrast, long term/permanent Potential Transformer installations can obtain more accurate measurements at the expense of high costs of Potential Transformers and highly accurate metering equipment.
Since power quality meters like the one described above have no ground connection, they are susceptible to the influence of adjacent lines on voltage measurements. The influence of these adjacent lines can create phase/power factor errors.
Some systems require multiple instruments to get both current and absolute voltage reading. No known hot stick mounted device is presently available that allows for simultaneous, accurate current and voltage measurement.
To compute power, simultaneous and accurate measurements of voltage and current are required. Since existing portable devices do not simultaneously measure both quantities, measurement of power (and reactive power and phase angle) are precluded.